This invention relates generally to the transfer of heat away from a hot body and is particularly directed to a conformable pad containing a thermally conductive material for removing heat from a packaged electronic device with which the pad is in contact.
Electronic circuitry and components generate heat during operation. Removal of this heat is critical for stable operation and long operating lifetimes. As circuit packaging densities increase, efficient heat removal has become even more critical.
Heat is removed from electronic devices by various means such as cooling fans, heat sinks, and bimetallic cooling arrangements, to name a few. Cooling fans require their own circuitry and thus increase the complexity and expense of the electronic apparatus. Heat sinks may be either of the metallic type such as comprised of aluminum or of the conformable type. Typically metallic sinks are mechanically attached to the electronic device from which heat is to be removed by means of thermally conductive greases, films or adhesives. Because of their rigid structure, thermal coupling between the electronic device and the metallic heat sink is generally limited to the planar surfaces of contact between the heat sink and electronic device. In order to increase the surface area of contact with the electronic device, some heat sinks are comprised of a conformable plastic pouch hermetically filled with an inert thermally conductive fluid. Although increasing the efficiency of heat transfer and removal, these latter heat sinks are subject to leakage of the thermally conductive fluid which not only ends heat dissipation by the device, but also contaminates the electronic apparatus with the thus leaked fluid. Leakage of the materials which are typically used in such conformable plastic pouch heat sinks, e.g., fluorinated compounds, is particularly undesirable from environmental considerations.
The aforementioned approaches to dissipating heat from electronic devices are intended for use in specific applications. For example, when several flat integrated circuits (ICs) are located on a single printed circuit (PC) board and contained in a metallic box to prevent electromagnetic interference (EMI) and radio frequency interference (RFI) radiation, the box sometimes is also used as a heat sink. However, a problem arises in thermally coupling the IC packages to the box. Because the volume of the box is generally too small to allow for fins or other conventional heat sink devices, the use of a conformable plastic pouch is sometimes required. However, these conformable plastic pouch heat sinks suffer from the leakage problem discussed above and are expensive, and the configuration of the metal box may require a custom-fitted, plastic pouch which further increases the cost. Providing the outer film layer of the conformable plastic pouch with an aluminum foil to attenuate EMI/RFI radiation renders the use of these conformable heat sink pouches too expensive for most industrial and consumer electronic devices.